Method and device for managing interface for supporting lte/nr interworking in wireless communication system

ABSTRACT

Provided is a method for supporting E-UTRAN-NR dual connectivity (EN-DC) indicating dual connectivity between Long-Term Evolution (LTE), that is, Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), and New Radio (NR) Access Technology (NR) in a wireless communication system. A first radio access network (RAN) node transmits an X2 configuration request message, including a first indication indicating that the first RAN node supports EN-DC, to a second RAN node, and receives an X2 configuration response message, including a second indication indicating that the second RAN node supports the EN-DC, from the second RAN node.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 16/476,022, filed on Jul.3, 2019, which is a National Stage application under 35 U.S.C. § 371 ofInternational Application No. PCT/KR2018/000164, filed on Jan. 4, 2018,which claims the benefit of U.S. Provisional Application No. 62/443,003,filed on Jan. 6, 2017. The disclosures of the prior applications areincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communication and, moreparticularly, to a method and device for managing an interface forsupporting interworking of 3rd generation partnership project (3GPP)long-term evolution (LTE) and new radio access technology (NR) amongwireless communication systems.

Related Art

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

Work has started in international telecommunication union (ITU) and 3GPPto develop requirements and specifications for new radio (NR) systems.The NR system may be called another name, e.g. new radio accesstechnology (new RAT). 3GPP has to identify and develop the technologycomponents needed for successfully standardizing the NR timelysatisfying both the urgent market needs, and the more long-termrequirements set forth by the ITU radio communication sector (ITU-R)international mobile telecommunications (IMT)-2020 process. Further, theNR should be able to use any spectrum band ranging at least up to 100GHz that may be made available for wireless communications even in amore distant future.

The NR targets a single technical framework addressing all usagescenarios, requirements and deployment scenarios including enhancedmobile broadband (eMBB), massive machine-type-communications (mMTC),ultra-reliable and low latency communications (URLLC), etc. The NR shallbe inherently forward compatible.

New architecture for a 5G core network including NR and 5G radio accessnetwork (RAN) may provide better services for user equipment (UE) interms of throughput and UE experience. Also, tight interworking ofLTE/NR is under discussion. dual/multiple connectivity capable ofimproving throughput of a UE according to the tight interworking ofLTE/NR may be used, and signaling for UE mobility may be simplified.

A method for more efficiently supporting tight interworking of LTE/NRmay be required.

SUMMARY OF THE INVENTION

The present invention provides a method and device for managing aninterface to support interworking of the 3GPP LTE and NR among wirelesscommunication systems. The present invention provides an improvedcell-specific procedure for dual/multiple connectivity in the 5G radioaccess network (RAN).

In an aspect, a method for performing an X2 setup procedure by a firstradio access network (RAN) node in a wireless communication system isprovided. The method includes transmitting an X2 setup request messageincluding a first indication indicating that the first RAN node supportsa evolved-UMTS terrestrial radio access (E-UTRAN)-new radio accessnetwork (NR) dual connectivity (EN-DC) to a second RAN node, andreceiving an X2 setup response message including a second indicationindicating that the second RAN node supports the EN-DC from the secondRAN node.

In another aspect, a first radio access network (RAN) node in a wirelesscommunication system is provided. The first RAN node includes a memory,and a processor, operably coupled to the memory. The processor transmitsan X2 setup request message including a first indication indicating thatthe first RAN node supports a evolved-UMTS terrestrial radio access(E-UTRAN)-new radio access network (NR) dual connectivity (EN-DC) to asecond RAN node, and receives an X2 setup response message including asecond indication indicating that the second RAN node supports the EN-DCfrom the second RAN node.

The first RAN node may be an eNodeB (eNB), and the second RAN node maybe a gNB. The first indication may correspond to a global eNB identifier(ID), and the second indication may correspond to a global gNB ID.

Alternatively, the first RAN node may be gNB, and the second RAN nodemay be an eNB. The first indication may correspond to a global gNB ID,and the second indication may correspond to a global eNB ID.

The X2 setup request message may be an EN-DC X2 setup request message,and the X2 setup response message may be an EN-DC X2 setup responsemessage.

The first RAN node may trigger a dual connectivity procedure related tothe EN-DC, based on the second indication.

Tight interworking of LTE/NR may be supported more efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows 3GPP LTE system architecture.

FIG. 2 shows an NG-RAN architecture.

FIG. 3 illustrates EN-DC architecture.

FIG. 4 illustrates the option 3/3 a of the disposition scenario fortight interworking of LTE/NR.

FIG. 5 illustrates the option 4/4 a of the disposition scenario fortight interworking of LTE/NR.

FIG. 6 illustrates the option 7/7 a of the disposition scenario fortight interworking of LTE/NR.

FIG. 7 illustrates a procedure for setting up an RAN interface accordingto one embodiment of the present invention.

FIG. 8 illustrates an RAN interface setup procedure according to anotherembodiment of the present invention.

FIG. 9 shows a method for performing an X2 setup procedure by a firstRAN node according to an embodiment of the present invention.

FIG. 10 illustrates an RAN interface setup procedure according toanother embodiment of the present invention.

FIG. 11 illustrates an RAN interface setup procedure according toanother embodiment of the present invention.

FIG. 12 shows a communication system to implement an embodiment of thepresent invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, in the present invention, a wireless communication systembased on a 3rd generation partnership project (3GPP) or institute ofelectrical and electronics engineers (IEEE) is mainly described.However, the present invention is not limited thereto, and the presentinvention may be applied to other wireless communication systems havingthe same characteristics to be described hereinafter.

FIG. 1 shows 3GPP LTE system architecture. Referring to FIG. 1, the 3GPPLTE system architecture includes one or more user equipment (UE; 10), anevolved-UMTS terrestrial radio access network (E-UTRAN) and an evolvedpacket core (EPC). The UE 10 refers to a communication equipment carriedby a user. The UE 10 may be fixed or mobile, and may be referred to asanother terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), anaccess point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10. An uplink (UL) denotes communication from the UE 10 to theeNB 20. A sidelink (SL) denotes communication between the UEs 10. In theDL, a transmitter may be a part of the eNB 20, and a receiver may be apart of the UE 10. In the UL, the transmitter may be a part of the UE10, and the receiver may be a part of the eNB 20. In the SL, thetransmitter and receiver may be a part of the UE 10.

The EPC includes a mobility management entity (MME) and a servinggateway (S-GW). The MME/S-GW 30 provides an end point of session andmobility management function for the UE 10. For convenience, MME/S-GW 30will be referred to herein simply as a “gateway,” but it is understoodthat this entity includes both the MME and S-GW. A packet data network(PDN) gateway (P-GW) may be connected to an external network.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)gateway (P-GW) and S-GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g. deep packet inspection), lawfulinterception, UE Internet protocol (IP) address allocation, transportlevel packet marking in the DL, UL and DL service level charging, gatingand rate enforcement, DL rate enforcement based on access point nameaggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 is connected to the eNB 20 via a Uu interface. The UEs 10 areconnected to each other via a PC5 interface. The eNBs 20 are connectedto each other via an X2 interface. Neighboring eNBs may have a meshednetwork structure that has the X2 interface. The eNB 20 is connected tothe gateway 30 via an S1 interface.

5G system is a 3GPP system consisting of 5G access network (AN), 5G corenetwork (CN) and UE. 5G access network is an access network comprising anext generation radio access network (NG-RAN) and/or non-3GPP accessnetwork connecting to a 5G core network. NG-RAN is a radio accessnetwork that supports one or more of the following options with thecommon characteristics that it connects to 5G core network:

1) Standalone new radio (NR).

2) NR is the anchor with E-UTRA extensions.

3) Standalone E-UTRA.

4) E-UTRA is the anchor with NR extensions.

FIG. 2 shows an NG-RAN architecture. Referring to FIG. 2, the NG-RANincludes at least one NG-RAN node. The NG-RAN node includes at least onegNB and/or at least one ng-eNB. The gNB provides NR user plane andcontrol plane protocol terminations towards the UE. The ng-eNB providesE-UTRA user plane and control plane protocol terminations towards theUE. The gNBs and ng-eNBs are interconnected with each other by means ofthe Xn interface. The gNBs and ng-eNBs are also connected by means ofthe NG interfaces to the 5G CN. More specifically, the gNBs and ng-eNBsare connected to the access and mobility management function (AMF) bymeans of the NG-C interface and to the user plane function (UPF) bymeans of the NG-U interface.

The gNB and ng-eNB host the following functions:

-   -   Functions for radio resource management: Radio bearer control,        radio admission control, connection mobility control, dynamic        allocation of resources to UEs in both uplink and downlink        (scheduling);    -   Internet protocol (IP) header compression, encryption and        integrity protection of data;    -   Selection of an AMF at UE attachment when no routing to an AMF        can be determined from the information provided by the UE;    -   Routing of user plane data towards UPF(s);    -   Routing of control plane information towards AMF;    -   Connection setup and release;    -   Scheduling and transmission of paging messages;    -   Scheduling and transmission of system broadcast information        (originated from the AMF or operations & maintenance (O&M));    -   Measurement and measurement reporting configuration for mobility        and scheduling;    -   Transport level packet marking in the uplink;    -   Session management;    -   Support of network slicing;    -   QoS flow management and mapping to data radio bearers;    -   Support of UEs in RRC_INACTIVE state;    -   Distribution function for non-assess stratum (NAS) messages;    -   Radio access network sharing;    -   Dual connectivity;    -   Tight interworking between NR and E-UTRA.

The AMF hosts the following main functions:

-   -   NAS signaling termination;    -   NAS signaling security;    -   AS security control;    -   Inter CN node signaling for mobility between 3GPP access        networks;    -   Idle mode UE reachability (including control and execution of        paging retransmission);    -   Registration area management;    -   Support of intra-system and inter-system mobility;    -   Access authentication;    -   Access authorization including check of roaming rights;    -   Mobility management control (subscription and policies);    -   Support of network slicing;    -   Session management function (SMF) selection.

The UPF hosts the following main functions:

-   -   Anchor point for Intra-/Inter-radio access technology (RAT)        mobility (when applicable);    -   External protocol data unit (PDU) session point of interconnect        to data network;    -   Packet routing & forwarding;    -   Packet inspection and user plane part of policy rule        enforcement;    -   Traffic usage reporting;    -   Uplink classifier to support routing traffic flows to a data        network;    -   Branching point to support multi-homed PDU session;    -   QoS handling for user plane, e.g. packet filtering, gating,        UL/DL rate enforcement;    -   Uplink traffic verification (service data flow (SDF) to QoS flow        mapping);    -   Downlink packet buffering and downlink data notification        triggering.

The SMF hosts the following main functions:

-   -   Session management;    -   UE IP address allocation and management;    -   Selection and control of UP function;    -   Configures traffic steering at UPF to route traffic to proper        destination;    -   Control part of policy enforcement and QoS;    -   Downlink data notification.

In what follows, multi-RAT dual connectivity will be described. NG-RANsupports multi-RAT dual connectivity configured so that a UE in theRRC_CONNECTED state with multiple RX/TX may use radio resources providedby two separate schedulers. Multi-RAT dual connectivity isgeneralization of the E-UTRA dual connectivity. Two separate schedulersare located at two different NG-RAN nodes connected to each otherthrough a non-ideal backhaul. One of the two different NG-RAN nodesperforms the role of a master node (MN), and the other one performs therole of a secondary node (SN). In other words, one scheduler is locatedat the MN while the other scheduler is located at the SN. The twodifferent NG-RAN nodes provide either the E-UTRA connectivity (when theNG-RAN node is an ng-eNB) or NR connectivity (when the NG-RAN node is agNB). The ng-eNB is a node that provides the NR user plane and controlplane protocol termination toward a UE and operates as an SN in theE-UTRAN-NR dual connectivity (EN-DC). The gNB is a node that providesthe E-UTRA user plane and control plane protocol termination toward a UEand is connected to 5G CN through an NG interface. The MN and SN areconnected to each other through a network interface, and at least the MNis connected to the core network. Although multi-RAT dual connectivityin the present specification has been designed based on a non-idealbackhaul between different nodes, the multi-RAT dual connectivity mayalso be used for an ideal backhaul.

FIG. 3 illustrates EN-DC architecture. The E-UTRAN supports multi-RATdual connectivity through EN-DC, where a UE is connected to one eNBoperating as an MN and one en-gNB operating as an SN. An eNB isconnected to EPC through S1 interface and connected to en-gNB through X2interface. The en-gNB may be connected to the EPC through S1-U interfaceand connected to a different en-gNB through X2-U interface.

The 5G CN also supports multi-RAT dual connectivity. An NG-RAN supportsNG-RAN E-UTRA-NR dual connectivity (NGEN-DC), where a UE is connected toone ng-eNB operating as an MN and one gNB operating as an SN. The ng-eNBis connected to the 5G CN, and the gNB is connected to the ng-eNBthrough Xn interface. Also, the NG-RAN supports NR-E-UTRA dualconnectivity (NE-DC), where a UE is connected to one gNB operating as anMN and one ng-eNB operating as an SN. The gNB is connected to the 5G CN,and ng-eNB is connected to the gNB through Xn interface.

To support the aforementioned multi-RAT dual connectivity and/or tightinterworking of LTE/NR, various disposition scenarios for LTE and NR maybe considered.

FIG. 4 illustrates the option 3/3 a of the disposition scenario fortight interworking of LTE/NR. Referring to FIG. 4, in the case of option3/3 a, LTE eNB is connected to the EPC together with a non-standaloneNR. In other words, the NR control plane is not directly connected tothe EPC but connected through the LTE eNB. The NR user plane isconnected to the EPC through the LTE eNB (option 3) or connecteddirectly through the S-1U interface (option 3 a). Option 3/3 acorresponds to the EN-DC architecture of FIG. 3.

FIG. 5 illustrates the option 4/4 a of the disposition scenario fortight interworking of LTE/NR. Referring to FIG. 5, in the case of option4/4 a, eNB is connected to the NGC together with a non-standaloneE-UTRA. In other words, the E-UTRA control plane is not directlyconnected to the NGC but connected through the gNB. The E-UTRA controlplane is connected to the NGC through the gNB (option 4) or connecteddirectly through the NG-U interface (option 4 a). Option 4/4 acorresponds to the option 3/3 a with the E-UTRA and NR exchanged.

FIG. 6 illustrates the option 7/7 a of the disposition scenario fortight interworking of LTE/NR. Referring to FIG. 6, in the case of option7/7 a, eLTE eNB (namely, ng-eNB) is connected to the NGC together with anon-standalone NR. In other words, the NR control plane is not directlyconnected to the NGC but connected through the eLTE eNB. The NR userplane is connected to the NGC through the eLTE eNB (option 7) orconnected directly through the NG-U interface (option 7 a).

A method for supporting multi-RAT dual connectivity according to theaforementioned various disposition scenarios is under discussion. Asdescribed above, it may be seen that there may be various options tochoose two nodes (for example, eNB, gNB, ng-eNB, en-gNB) performing themulti-RAT dual connectivity operation. Therefore, which option to useamong the various disposition scenario options still needs to bedetermined.

More specifically, in the legacy LTE-based system, evolved packet system(EPS) bearer/E-UTRAN radio access bearer (E-RAB) and quality of service(QoS) are used, which corresponds to the option 3/3 a for the case ofdata packets. This is so because in the case of option 3/3 a, EPS is thecore network. However, in the case of option 4/4 a and 7/7a, newfeatures such as a newly introduced flow concept, flow-QoS mapping rule,RRC signaling, and UE capability negotiation among nodes may be adopted.This is so because NGC is the core network for the options 4/4 a and 7/7a. Therefore, it may be conjectured that a procedure for triggering anoffloading procedure (namely multi-RAT dual connectivity) is differentfrom a dual connectivity procedure of the legacy LTE. In other words,depending on the various disposition scenario options for multi-RAT dualconnectivity, it may not be easy for an RAN node to determine a methodfor triggering a dual connectivity procedure. The present inventionproposes a method for solving the aforementioned problem.

1. First Embodiment

FIG. 7 illustrates a procedure for setting up an RAN interface accordingto one embodiment of the present invention. In the present embodiment,it is assumed that RAN node 1 is eNB, and RAN node 2 is gNB. However,the assumption is only an example, and RAN node 1 and RAN node 2 may beone of eNB, gNB, ng-eNB, and en-gNB. Also, in the present embodiment, itis assumed that the RAN interface of the RAN node 1 and RAN node 2 is X2interface. However, this assumption is also an example, and variousother names may be used to refer to the RAN interface of the RAN node 1and RAN node 2 (for example, Xn interface). In the present embodiment,the RAN node 1 triggers a procedure for setting up the RAN interface.

When the RAN interface between the RAN node 1 and RAN node 2 is setup,if the RAN node 1 supports the option 3/3 a architecture for LTE/NRinterworking, the RAN node 1 may want to know whether a target node alsosupports the option 3/3 a architecture for LTE/NR interworking. This isso because depending on whether a target node supports the option 3/3 aarchitecture for LTE/NR interworking, different messages may be used fortriggering a dual connectivity procedure.

Accordingly, in step S100, the RAN node 1 transmits an RAN interfacesetup request message to the RAN node 2. The RAN interface setup requestmessage may include an indication indicating that the RAN node 1supports the option 3/3 a. Also, the RAN interface setup request messagemay include an indication requesting reporting whether a target node(namely, RAN node 2) of the RAN interface setup request message supportsthe option 3/3 a. Also, the RAN interface setup request message mayinclude an enhanced eNB ID of the RAN node 1. The enhanced eNB ID of theRAN node 1 may be a global eNB ID of the RAN node 1. The indicationindicating that the RAN node 1 supports the option 3/3 a may beimplemented by the enhanced eNB ID of the RAN node 1 or by the globaleNB ID of the RAN node 1. In other words, the enhanced eNB ID or globaleNB ID of the RAN node 1 may implicitly indicate that the RAN node 1supports the option 3/3 a. The RAN interface setup request message maybe implemented by an existing message or a new message of the X2interface or implemented by a new message of a new interface.

The RAN node 2, which has received an indication indicating that the RANnode 1 supports the option 3/3 a and/or an RAN interface setup requestmessage including the enhanced eNB ID (or global eNB ID) of the RAN node1, may take into account, for a UE-specific procedure, the indicationindicating that the RAN node 1 supports the option 3/3 a and/or theenhanced eNB ID (or global eNB ID) of the RAN node 1. For example, theRAN node 2 may use the indication indicating that the RAN node 1supports the option 3/3 a and/or the enhanced eNB ID (or global eNB ID)of the RAN node 1 for a dual connectivity procedure or multipleconnectivity procedure.

Also, in step S102, the RAN node 2 transmits an RAN interface setupresponse message to the RAN node 1. If the received RAN interface setuprequest message includes an indication requesting reporting whether theRAN node 2 supports the option 3/3 a, the RAN interface setup responsemessage may include an indication indicating that the RAN node 2supports the option 3/3 a. The indication indicating that the RAN node 2supports the option 3/3 a may be implemented by the global gNB ID of theRAN node 2. In other words, the global gNB ID of the RAN node 2 mayimplicitly indicate that the RAN node 2 supports the option 3/3 a. TheRAN interface setup response message may be implemented by an existingmessage or a new message of the X2 interface or implemented by a newmessage of a new interface.

The RAN node 1, which has received an RAN interface setup responsemessage including an indication indicating that the RAN node 2 supportsthe option 3/3 a and/or a global gNB ID of the RAN node 2, may perform asuitable operation based on the indication indicating that the RAN node2 supports the option 3/3 a and/or the global gNB ID of the RAN node 2.For example, based on the indication indicating that the RAN node 2supports the option 3/3 a and/or the global gNB ID of the RAN node 2,the RAN node 1 may trigger a new dual connectivity proceduredistinguished from the legacy LTE dual connectivity procedure. Dependingon the type of dual connectivity procedure, whether UE capability,flow-data ratio bearer (DRB) mapping rule, etc., have to be included inthe SeNB addition/modification message may be determined. Also, the RANnode 1 may determine the QoS type for a PDU session during the SeNBaddition/modification procedure differently according to the type of thedual connectivity procedure. Meanwhile, the RAN interface setup responsemessage received at step S102 may include an existing eNB ID, which maybe ignored by the RAN node 1.

FIG. 8 illustrates an RAN interface setup procedure according to anotherembodiment of the present invention. In the present embodiment, it isassumed that RAN node 1 is eNB, and RAN node 2 is gNB. However, theassumption is only an example, and the RAN node 1 and RAN node 2 may beany one of eNB, gNB, ng-eNB, and en-gNB. Also, the present embodimentassumes that the RAN interface of the RAN node 1 and RAN node 2 is X2interface. However, the assumption is also a mere example, and the RANinterface between the RAN node 1 and RAN node 2 may be called by variousother names (for example, Xn interface). In the present embodiment, theRAN node 2 triggers the RAN interface setup procedure.

When the RAN interface is setup between the RAN node 1 and RAN node 2,if the RAN node 2 supports the architecture of option 3/3 a for LTE/NRinterworking, the RAN node 2 may want to know whether a target node alsosupports the architecture of option 3/3 a for LTE/NR interworking. Thisis so because a different message may be used for the dual connectivityprocedure depending on whether the target node supports the architectureof option 3/3 a for LTE/NR interworking.

Accordingly, in step S110, the RAN node 2 transmits an RAN interfacesetup request message to the RAN node 1. The RAN interface setup requestmessage may include an indication indicating that the RAN node 2supports the option 3/3 a. Also, the RAN interface setup request messagemay include an indication requesting reporting whether a target node(namely RAN node 1) of the RAN interface setup request message supportsthe option 3/3 a. Also, the RAN interface setup request message mayinclude a global gNB ID of the RAN node 2. The indication indicatingthat the RAN node 2 supports the option 3/3 a may be implemented by theglobal gNB ID of the RAN node 2. In other words, the global gNB ID ofthe RAN node 2 may implicitly indicate that the RAN node 2 supports theoption 3/3 a. The RAN interface setup request message may be implementedby an existing message or a new message of the X2 interface orimplemented by a new message of a new interface.

The RAN node 1, which has received an RAN interface setup requestmessage including an indication indicating that the RAN node 2 supportsthe option 3/3 a and/or a global gNB ID of the RAN node 2, may take intoaccount the indication indicating that the RAN node 2 supports theoption 3/3 a and/or the global gNB ID of the RAN node 2 for aUE-specific procedure. For example, the RAN node 1 may use an indicationindicating that the RAN node 2 supports the option 3/3 a and/or theglobal gNB ID of the RAN node 2 for a dual connectivity procedure ormultiple connectivity procedure.

Also, in step S112, the RAN node 1 transmits an RAN interface setupresponse message to the RAN node 2. If the received RAN interface setuprequest message includes an indication requesting reporting whether theRAN node 1 supports the option 3/3 a, the RAN interface setup responsemessage may include an indication indicating that the RAN node 1supports the option 3/3 a. The indication indicating that the RAN node 1supports the option 3/3 a may be implemented by the enhanced eNB ID ofthe RAN node 1. The enhanced eNB ID of the RAN node 1 may be the globaleNB ID of the RAN node 1. In other words, the enhanced eNB ID (or globaleNB ID) of the RAN node 1 may implicitly indicate that the RAN node 1supports the option 3/3 a. The RAN interface setup response message maybe implemented by an existing message or a new message of the X2interface or implemented by a new message of a new interface.

The RAN node 2, which has received an RAN interface setup responsemessage including an indication indicating that the RAN node 1 supportsthe option 3/3 a and/or an enhanced eNB ID (or global eNB ID) of the RANnode 1, may perform a suitable operation based on the indicationindicating that the RAN node 1 supports the option 3/3 a and/or theenhanced eNB ID (or global eNB ID) of the RAN node 1. For example, basedon the indication indicating that the RAN node 1 supports the option 3/3a and/or the enhanced eNB ID (or global eNB ID) of the RAN node 1, theRAN node 2 may trigger a new dual connectivity procedure distinguishedfrom the legacy LTE dual connectivity procedure. Depending on the typeof dual connectivity procedure, whether UE capability, flow-DRB mappingrule, etc., have to be included in the SeNB addition/modificationmessage may be determined. Also, the RAN node 2 may determine the QoStype for a PDU session during the SeNB addition/modification proceduredifferently according to the type of the dual connectivity procedure.Meanwhile, the RAN interface setup response message received at stepS112 may include an existing eNB ID, which may be ignored by the RANnode 2.

The RAN interface setup procedure described with reference to FIG. 7 or8 may be the EN-DC X2 setup procedure. The purpose of the EN-DC X2 setupprocedure is to exchanged application level configuration data requiredfor an eNB and en-gNB to properly inter-operate on the X2 interface. TheEN-DC X2 setup procedure deletes existing application levelconfiguration data of two nodes and substitute received data for thedeleted data. The EN-DC X2 setup procedure reconfigures the X2 interfaceas in the reconfiguration procedure. The EN-DC X2 setup procedure usesnon-UE-specific signaling.

If the RAN interface setup procedure described with reference to FIG. 7or 8 is the EN-DC X2 setup procedure, the RAN interface setup requestmessage transmitted by the RAN node 1 of FIG. 7 and the RAN interfacesetup request message transmitted by the RAN node 2 of FIG. 8 may be theEN-DC X2 setup request message described in the Table 1 below. The EN-DCX2 setup request message is a message transmitted to a neighboringE-UTRAN node by an initiating E-UTRAN node, and both of the two nodesmay interact with each other for the EN-DC. The EN-DC X2 setup requestmessage delivers initialization information about transport networklayer (TNL) association.

TABLE 1 IE type IE/Group and Semantics Assigned Name Presence Rangereference description Criticality Criticality Message Type M 9.2.13 YESreject CHOICE Initiating M NodeType >eNB >>Global eNB ID M 9.2.22 YESreject >en-gNB >>Global en-gNB ID M <ref> YES reject >>List of Served NR1 . . . list of cells YES reject Cells <maxCellinen served by the gNB>engNB >>>Served NR Cell M 9.2.y — — Information >>>NR Neighbour O 9.2.xNR YES ignore Information neighbors

Referring to Table 1, the EN-DC X2 setup request message may include aglobal eNB ID (“Global eNB ID” information element (IE)) or global eNBID (“global en-gNB ID” IE) according to the entity that transmits themessage. More specifically, if the eNB transmits the EN-DC X2 setuprequest message according to the embodiment of FIG. 7, the EN-DC X2setup request message may include the global eNB ID. If the gNBtransmits the EN-DC X2 setup request message according to the embodimentof FIG. 8, the EN-DC X2 setup request message may include the global gNBID.

Also, the RAN interface setup response message transmitted by the RANnode 2 of FIG. 7 or the RAN interface setup response message transmittedby the RAN node 1 of FIG. 8 may be the EN-DC X2 setup response messagedescribed in the Table 2 below. The EN-DC X2 setup response message is amessage transmitted to an initiating E-UTRAN node by a neighboringE-UTRAN node, and both of the two nodes may interact with each other forthe EN-DC. The EN-DC X2 setup response message delivers initializationinformation about transport network layer (TNL) association.

TABLE 2 IE type IE/Group and Semantics Assigned Name Presence Rangereference description Criticality Criticality Message Type M 9.2.13 YESreject CHOICE Responding M NodeType >eNB >>Global eNB ID M 9.2.22 YESreject >en-gNB >>Global en-gNB ID M <ref> YES reject >>List of 1 . . .List of cells Served NR <maxCellinen served by the YES reject Cells gNB>en-gNB >>>Served NR Cell M 9.2.y — — Information >>>NR Neighbour O 9.2.xNR YES ignore Information neighbors

Referring to Table 2, the EN-DC X2 setup response message may include aglobal eNB ID (“Global eNB ID” information element (IE)) or global eNBID (“global en-gNB ID” IE) according to the entity that transmits themessage. More specifically, if the gNB transmits the EN-DC X2 setupresponse message according to the embodiment of FIG. 7, the EN-DC X2setup response message may include the global gNB ID. If the eNBtransmits the EN-DC X2 setup response message according to theembodiment of FIG. 8, the EN-DC X2 setup response message may includethe global eNB ID.

FIG. 9 shows a method for performing an X2 setup procedure by a firstRAN node according to an embodiment of the present invention. Thepresent invention described in FIGS. 7 and 8 may be applied to thisembodiment.

In step S120, the first RAN node transmits an X2 setup request messageincluding a first indication indicating that the first RAN node supportsan EN-DC to a second RAN node. The X2 setup request message may be anEN-DC X2 setup request message. The EN-DC X2 setup request message mayfollow Table 1 described above. In step S122, the first RAN nodereceives an X2 setup response message including a second indicationindicating that the second RAN node supports the EN-DC from the secondRAN node. The X2 setup response message may be an EN-DC X2 setupresponse message. The EN-DC X2 setup response message may follow Table 2described above. The first RAN node may trigger a dual connectivityprocedure related to the EN-DC, based on the second indication.

The first RAN node may be an eNB, and the second RAN node may be a gNB.In this case, the first indication may correspond to a global eNB ID,and the second indication may correspond to a global gNB ID.

Alternatively, the first RAN node may be gNB, and the second RAN nodemay be an eNB. In this case, the first indication may correspond to aglobal gNB ID, and the second indication may correspond to a global eNBID.

According to an embodiment of the present invention, new architecturefor a 5G core network including NR and 5G RAN may provide betterservices for UE in terms of throughput and UE experience. Also, tightinterworking of LTE/NR may be performed more easily according todual/multiple connectivity that may be triggered by the MN together witha suitable procedure. Also, dual/multiple connectivity capable ofimproving throughput of a UE according to the tight interworking ofLTE/NR may be used, and signaling for UE mobility may be simplified.

2. Second Embodiment

FIG. 10 illustrates an RAN interface setup procedure according toanother embodiment of the present invention. In the present embodiment,it is assumed that RAN node 1 is eNB, and RAN node 2 is gNB. However,the assumption is only an example, and RAN node 1 and RAN node 2 may beone of eNB, gNB, ng-eNB, and en-gNB. Also, in the present embodiment, itis assumed that the RAN interface of the RAN node 1 and RAN node 2 is Xninterface. However, this assumption is also an example, and variousother names may be used to refer to the RAN interface of the RAN node 1and RAN node 2 (for example, Xn interface). In the present embodiment,the RAN node 1 triggers a procedure for setting up the RAN interface.

When the RAN interface between the RAN node 1 and RAN node 2 is setup,if the RAN node 1 supports the option 3/3 a architecture and/or option4/4 a architecture and/or option 7/7 a architecture for LTE/NRinterworking, the RAN node 1 may want to know whether a target node alsosupports the option 3/3 a architecture and/or option 4/4 a architectureand/or option 7/7 a architecture for LTE/NR interworking. This is sobecause depending on whether a target node supports the option 3/3 aarchitecture and/or option 4/4 a architecture and/or option 7/7 aarchitecture for LTE/NR interworking, different messages may be used fortriggering a dual connectivity procedure.

Accordingly, in step S200, the RAN node 1 transmits an RAN interfacesetup request message to the RAN node 2. The RAN interface setup requestmessage may include an indication indicating that the RAN node 1supports the option 3/3 a. Also, the RAN interface setup request messagemay include an indication indicating that the RAN node 1 supports theoption 4/4 a. Also, the RAN interface setup request message may includean indication indicating that the RAN node 1 supports the option 7/7 a.Also, the RAN interface setup request message may include an indicationrequesting reporting whether a target node (namely RAN node 2) of theRAN interface setup request message supports the option 3/3 a and/oroption 4/4 a and/or option 7/7 a. Also, the RAN interface setup requestmessage may include an enhanced eNB ID of the RAN node 1. The enhancedeNB ID of the RAN node 1 may be a global eNB ID of the RAN node 1. TheRAN interface setup request message may be implemented by an existingmessage or a new message of the Xn interface or implemented by a newmessage of a new interface.

The RAN node 2, which has received the RAN interface setup requestmessage, may take into account an indication indicating that the RANnode 1 supports the option 3/3 a and/or an indication indicating thatthe RAN node 1 supports the option 4/4 a and/or an indication indicatingthat the RAN node 1 supports the option 7/7 a and/or an enhanced eNB ID(or global eNB ID) of the RAN node 1 for a UE-specific procedure. Forexample, for a dual connectivity procedure or multiple connectivityprocedure, the RAN node 2 may use an indication indicating that the RANnode 1 supports the option 3/3 a and/or an indication indicating thatthe RAN node 1 supports the option 4/4 a and/or an indication indicatingthat the RAN node 1 supports the option 7/7 a and/or an enhanced eNB ID(or global eNB ID) of the RAN node 1.

Also, at step S202, the RAN node 2 transmits an RAN interface setupresponse message to the RAN node 1. If the received RAN interface setuprequest message includes an indication requesting reporting whether theRAN node 2 supports the option 3/3 a and/or option 4/4 a and/or option7/7 a, the RAN interface setup response message may include anindication indicating that the RAN node 2 supports the option 3/3 aand/or an indication indicating that the RAN node 2 supports the option4/4 a and/or an indication indicating that the RAN node 2 supports theoption 7/7 a. Also, the RAN interface setup response message may includea global gNB ID of the Xn interface. The RAN interface setup responsemessage may be implemented by an existing message or a new message ofthe Xn interface or implemented by a new message of a new interface.

The RAN node 1, which has received an RAN interface setup responsemessage, may perform a suitable operation based on the indicationindicating that the RAN node 2 supports the option 3/3 a and/or theindication indicating that the RAN node 2 supports the option 4/4 aand/or the indication indicating that the RAN node 2 supports the option7/7 a and/or the global gNB ID of the RAN node 2. For example, based onthe indication indicating that the RAN node 2 supports the option 3/3 aand/or the indication indicating that the RAN node 2 supports the option4/4 a and/or the indication indicating that the RAN node 2 supports theoption 7/7 a and/or the global gNB ID of the RAN node 2, the RAN node 1may trigger a new dual connectivity procedure distinguished from thelegacy LTE dual connectivity procedure. Depending on the type of dualconnectivity procedure, whether UE capability, flow-DRB mapping rule,etc., have to be included in the SeNB addition/modification message maybe determined. Also, the RAN node 1 may determine the QoS type for a PDUsession during the SeNB addition/modification procedure differentlyaccording to the type of the dual connectivity procedure.

Meanwhile, in the embodiment above, different message sets may be usedfor the option 3/3 a, option 4/4 a, and option 7/7 a, respectively.

FIG. 11 illustrates an RAN interface setup procedure according toanother embodiment of the present invention. In the present embodiment,it is assumed that RAN node 1 is eNB, and RAN node 2 is gNB. However,the assumption is only an example, and RAN node 1 and RAN node 2 may beone of eNB, gNB, ng-eNB, and en-gNB. Also, in the present embodiment, itis assumed that the RAN interface of the RAN node 1 and RAN node 2 is Xninterface. However, this assumption is also an example, and variousother names may be used to refer to the RAN interface of the RAN node 1and RAN node 2 (for example, Xn interface). In the present embodiment,the RAN node 2 triggers a procedure for setting up the RAN interface.

When the RAN interface between the RAN node 1 and RAN node 2 is setup,if the RAN node 2 supports the option 3/3 a architecture and/or option4/4 a architecture and/or option 7/7 a architecture for LTE/NRinterworking, the RAN node 2 may want to know whether a target node alsosupports the option 3/3 a architecture and/or option 4/4 a architectureand/or option 7/7 a architecture for LTE/NR interworking. This is sobecause depending on whether a target node supports the option 3/3 aarchitecture and/or option 4/4 a architecture and/or option 7/7 aarchitecture for LTE/NR interworking, different messages may be used fortriggering a dual connectivity procedure.

Accordingly, in step S210, the RAN node 2 transmits an RAN interfacesetup request message to the RAN node 1. The RAN interface setup requestmessage may include an indication indicating that the RAN node 2supports the option 3/3 a. Also, the RAN interface setup request messagemay include an indication indicating that the RAN node 2 supports theoption 4/4 a. Also, the RAN interface setup request message may includean indication indicating that the RAN node 2 supports the option 7/7 a.Also, the RAN interface setup request message may include an indicationrequesting reporting whether a target node (namely RAN node 1) of theRAN interface setup request message supports the option 3/3 a and/oroption 4/4 a and/or option 7/7 a. Also, the RAN interface setup requestmessage may include a global gNB ID of the RAN node 2. The enhanced eNBID of the RAN node 1 may be a global eNB ID of the RAN node 1. The RANinterface setup request message may be implemented by an existingmessage or a new message of the Xn interface or implemented by a newmessage of a new interface.

The RAN node 1, which has received the RAN interface setup requestmessage, may take into account an indication indicating that the RANnode 2 supports the option 3/3 a and/or an indication indicating thatthe RAN node 2 supports the option 4/4 a and/or an indication indicatingthat the RAN node 2 supports the option 7/7 a and/or a global gNB ID ofthe RAN node 2 for a UE-specific procedure. For example, for a dualconnectivity procedure or multiple connectivity procedure, the RAN node1 may use an indication indicating that the RAN node 2 supports theoption 3/3 a and/or an indication indicating that the RAN node 2supports the option 4/4 a and/or an indication indicating that the RANnode 2 supports the option 7/7 a and/or a global gNB ID of the RAN node2.

Also, at step S212, the RAN node 1 transmits an RAN interface setupresponse message to the RAN node 2. If the received RAN interface setuprequest message includes an indication requesting reporting whether theRAN node 1 supports the option 3/3 a and/or option 4/4 a and/or option7/7 a, the RAN interface setup response message may include anindication indicating that the RAN node 1 supports the option 3/3 aand/or an indication indicating that the RAN node 1 supports the option4/4 a and/or an indication indicating that the RAN node 1 supports theoption 7/7 a. Also, the RAN interface setup response message may includean enhanced eNB ID of the RAN node 1. The eNB ID of the RAN node 1 maybe a global eNB ID. The RAN interface setup response message may beimplemented by an existing message or a new message of the Xn interfaceor implemented by a new message of a new interface.

The RAN node 2, which has received an RAN interface setup responsemessage, may perform a suitable operation based on the indicationindicating that the RAN node 1 supports the option 3/3 a and/or theindication indicating that the RAN node 1 supports the option 4/4 aand/or the indication indicating that the RAN node 1 supports the option7/7 a and/or the enhanced eNB ID (or global eNB ID) of the RAN node 1.For example, based on the indication indicating that the RAN node 1supports the option 3/3 a and/or the indication indicating that the RANnode 1 supports the option 4/4 a and/or the indication indicating thatthe RAN node 1 supports the option 7/7 a and/or the enhanced eNB ID (orglobal eNB ID) of the RAN node 1, the RAN node 2 may trigger a new dualconnectivity procedure distinguished from the legacy LTE dualconnectivity procedure. Depending on the type of dual connectivityprocedure, whether UE capability, flow-DRB mapping rule, etc., have tobe included in the SeNB addition/modification message may be determined.Also, the RAN node 2 may determine the QoS type for a PDU session duringthe SeNB addition/modification procedure differently according to thetype of the dual connectivity procedure.

Meanwhile, in the embodiment above, different message sets may be usedfor the option 3/3 a, option 4/4 a, and option 7/7 a, respectively.

According to an embodiment of the present invention, new architecturefor a 5G core network including NR and 5G RAN may provide betterservices for UE in terms of throughput and UE experience. Also, tightinterworking of LTE/NR may be performed more easily according todual/multiple connectivity that may be triggered by the MN together witha suitable procedure. Also, dual/multiple connectivity capable ofimproving throughput of a UE according to the tight interworking ofLTE/NR may be used, and signaling for UE mobility may be simplified.

Meanwhile, the present invention may be used to help RAN nodes trigger amobility/handover procedure among various types of RAN nodes (namelyeNB, gNB, ng-eNB, en-gNB).

FIG. 12 shows a communication system to implement an embodiment of thepresent invention.

A first RAN node 800 includes a processor 810, a memory 820 and atransceiver 830. The processor 810 may be configured to implementproposed functions, procedures and/or methods described in thisdescription. Layers of the radio interface protocol may be implementedin the processor 810. The memory 820 is operatively coupled with theprocessor 810 and stores a variety of information to operate theprocessor 810. The transceiver 830 is operatively coupled with theprocessor 810, and transmits and/or receives a radio signal.

A second RAN node 900 includes a processor 910, a memory 920 and atransceiver 930. The processor 910 may be configured to implementproposed functions, procedures and/or methods described in thisdescription. Layers of the radio interface protocol may be implementedin the processor 910. The memory 920 is operatively coupled with theprocessor 910 and stores a variety of information to operate theprocessor 910. The transceiver 930 is operatively coupled with theprocessor 910, and transmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What is claimed is:
 1. A method for performing an X2 setup procedure bya second radio access network (RAN) node in a wireless communicationsystem, the method comprising: receiving, from a first RAN node, an X2setup request message including a global identifier (ID) of the firstRAN node; and transmitting, to the first RAN node, an X2 setup responsemessage including a global ID of the second RAN node, wherein the X2setup procedure is initiated to exchange configuration data needed forthe first RAN node and the second RAN node to inter-operate over an X2interface, wherein the first RAN node is an RAN node among either aneNodeB (eNB) of a long-term evolution (LTE) or a gNB of a new radioaccess technology (NR), wherein the second RAN node is an RAN nodedifferent from the first RAN node among either the eNB or the gNB,wherein the global ID of the first RAN node and the global ID of thesecond RAN node are determined based on whether the first RAN node andthe second RAN node are the eNB or the gNB respectively, and wherein theX2 setup request message and the X2 setup response message aretransmitted and received for an evolved-UMTS terrestrial radio access(E-UTRAN)-NR dual connectivity (EN-DC) between the LTE and the NR. 2.The method of claim 1, wherein the first RAN node is the eNB, andwherein the second RAN node is the gNB.
 3. The method of claim 2,wherein the global ID of the first RAN node includes a global eNB ID,and wherein the global ID of the second RAN node includes a global gNBID.
 4. The method of claim 1, wherein the first RAN node is the gNB, andwherein the second RAN node is the eNB.
 5. The method of claim 4,wherein the global ID of the first RAN node includes a global gNB ID,and wherein the global ID of the second RAN node includes a global eNBID.
 6. The method of claim 1, wherein the X2 setup request message is anEN-DC X2 setup request message, and wherein the X2 setup responsemessage is an EN-DC X2 setup response message.
 7. The method of claim 1,further comprising triggering a dual connectivity procedure related tothe EN-DC, based on the X2 setup response message.
 8. A second radioaccess network (RAN) node in a wireless communication system, the secondRAN node comprising: a memory; and a processor, operably coupled to thememory, and configured to: control the second RAN node to receive, froma first RAN node, an X2 setup request message including a globalidentifier (ID) of the first RAN node, and control the second RAN nodeto transmit, to the second RAN node, an X2 setup response messageincluding a global ID of the second RAN node, wherein an X2 setupprocedure is initiated to exchange configuration data needed for thefirst RAN node and the second RAN node to inter-operate over an X2interface, wherein the first RAN node is an RAN node among either aneNodeB (eNB) of a long-term evolution (LTE) or a gNB of a new radioaccess technology (NR), wherein the second RAN node is an RAN nodedifferent from the first RAN node among either the eNB or the gNB,wherein the global ID of the first RAN node and the global ID of thesecond RAN node are determined based on whether the first RAN node andthe second RAN node are the eNB or the gNB respectively, and wherein theX2 setup request message and the X2 setup response message aretransmitted and received for an evolved-UMTS terrestrial radio access(E-UTRAN)-NR dual connectivity (EN-DC) between the LTE and the NR. 9.The first RAN node of claim 8, wherein the first RAN node is the eNB,and wherein the second RAN node is the gNB.
 10. The first RAN node ofclaim 9, wherein the global ID of the first RAN node includes a globaleNB ID, and wherein the global ID of the second RAN node includes aglobal gNB ID.
 11. The first RAN node of claim 8, wherein the first RANnode is the gNB, and wherein the second RAN node is the eNB.
 12. Thefirst RAN node of claim 11, wherein the global ID of the first RAN nodeincludes a global gNB ID, and wherein the global ID of the second RANnode includes a global eNB ID.
 13. The first RAN node of claim 8,wherein the X2 setup request message is an EN-DC X2 setup requestmessage, and wherein the X2 setup response message is an EN-DC X2 setupresponse message.
 14. The first RAN node of claim 8, wherein theprocessor further triggers a dual connectivity procedure related to theEN-DC, based on X2 setup response message.
 15. A computer-readablemedium having stored thereon a plurality of instructions, which, whenexecuted by a processor of a second radio access network (RAN) node,cause the second RAN node to: receive, from a first RAN node, an X2setup request message including a global identifier (ID) of the firstRAN node; and transmit, to the first RAN node, an X2 setup responsemessage including a global ID of the second RAN node, wherein an X2setup procedure is initiated to exchange configuration data needed forthe first RAN node and the second RAN node to inter-operate over an X2interface, wherein the first RAN node is an RAN node among either aneNodeB (eNB) of a long-term evolution (LTE) or a gNB of a new radioaccess technology (NR), wherein the second RAN node is an RAN nodedifferent from the first RAN node among either the eNB or the gNB,wherein the global ID of the first RAN node and the global ID of thesecond RAN node are determined based on whether the first RAN node andthe second RAN node are the eNB or the gNB respectively, and wherein theX2 setup request message and the X2 setup response message aretransmitted and received for an evolved-UMTS terrestrial radio access(E-UTRAN)-NR dual connectivity (EN-DC) between the LTE and the NR. 16.The computer-readable medium of claim 15, wherein the first RAN node isthe eNB, and wherein the second RAN node is the gNB.
 17. Thecomputer-readable medium of claim 16, wherein the global ID of the firstRAN node includes a global eNB ID, and wherein the global ID of thesecond RAN node includes a global gNB ID.
 18. The computer-readablemedium of claim 15, wherein the first RAN node is the gNB, and whereinthe second RAN node is the eNB.
 19. The computer-readable medium ofclaim 18, wherein the global ID of the first RAN node includes a globalgNB ID, and wherein the global ID of the second RAN node includes aglobal eNB ID.
 20. The computer-readable medium of claim 15, wherein theX2 setup request message is an EN-DC X2 setup request message, andwherein the X2 setup response message is an EN-DC X2 setup responsemessage.